The features presented in this section are undoubtedly not for the
casual PVM user, but for tool developers. Collaboration with other
research groups and the addition of these features has had a positive
effect on PVM. The protocols are now conceptually ``cleaner'' than
they were before. We have shown that the system can be made more
powerful and general without increasing the amount of code, by making
it dynamically extensible. The result has been directly useful to all
the projects involved, and we hope it will have even more widespread
application as the interfaces become more stable and other researchers
take advantage of them.